Spin stabilized projectile with metal band

ABSTRACT

The invention concerns a spin-stabilized projectile provided with a metal band (4). The projectile comprises a projectile body divided into a front main portion (1) and a rear main portion (2). The main portions are joined at the stern part of the projectile by means of a joint (3). The band is soldered or brazed with its inner surface and front flank surface onto an essentially cylindrical surface (6) and a rearwardly directed annular flank surface (5) of a shoulder which is formed in the rear end of the front main portion and extends round the projectile and which preferably has a length which is the same as the width of the band.

TECHNICAL FIELD

The invention relates to a spin-stabilised projectile, provided with aband. The body of the projectile consists of two main portions which arejoined by means of a joint at the stern part of the projectile, wherethe band is attached to the projectile body. The band is made of a metalalloy which is softer than the material of the projectile body, e.g. acopper alloy.

PRIOR ART

Spin-stabilised projectiles are usually provided with a band of a softeralloy, e.g. copper, for sealing against propellant gases and forimparting a spin to the projectile. When the projectile begins to beadvanced through a rifled barrel, grooves are pressed into the band bythe rifle ridges which then act as guides for the grooves. As theprojectile is accelerated through the bore, the helical rifle ridgesforce the band and thus the projectile to spin. The indisposition,caused by the spin acceleration, to spinning of the projectile resultsin great stress between the band and the projectile body. In aconventional fashion, the band is fixed in a groove turned in theprojectile body. The band is shrunk by being pressed radially inwards toembossing of the material so as to get a firm grip which is improved bythe bottom of the groove being formed with driving flutes, into whichthe band material is pressed.

Recently, one has begun to use weapons for projectiles acting withkinetic energy. Since this action is dependent on the mass and strikingspeed of the projectile, these weapons are used together with heavierprojectiles and a higher firing speed than in prior-art technique. Ahigher firing speed is also desired for an increased firing range. Owingto the higher trajectory speed, a higher speed of spinning of theprojectile is required for maintained stability. A higher spinning speedis also obtained when older barrels with unchanged rifles are used at anincreased firing speed. To make it possible to obtain a higher spinningspeed at an unchanged or relatively small increase of the length of thebarrel, it is necessary for the spinning of the projectile to acceleratemore when driven through the barrel as compared with firing according toearlier technique.

By increasing the mass as well as the spinning acceleration of theprojectile, the stresses in the connection between the band and theprojectile body, which are caused by the above-mentioned factors, haveincreased significantly. The stresses have become so great that bandsfixed according to prior-art technique have lost their hold and slid intheir grooves of the above-mentioned type.

SUMMARY OF THE INVENTION

Technical problem

The object of the invention is to provide a spin-stabilised projectilewith a metal band as mentioned by way of introduction. The projectilehas, inter alia, the following properties:

improved fixing of the metal band

rational manufacture of the projectile

Solution

This object is achieved by the projectile of the present invention.

A metal band usually is of essentially rectangular cross-section. Theboundary surface consists of four surfaces: Inner and outer surfacedenominated according to the inner and outer diameter of the metal bandas well as front and rear flank surface.

The invention suggests that the metal band be fixed by soldering orbrazing to the front main portion of the projectile body. In order toaccomplish a sufficiently strong connection, both the inner surface ofthe metal band and as much as possible of its front flank surface areused for soldering or brazing. These surfaces are fixed to thecorresponding receiving surfaces of said front main portion, which aredesigned as a stepped shoulder extending round the stern of the mainportion. This shoulder thus comprises a rearwardly directed flanksurface and a substantially cylindrical surface extending astern atleast as far as the width of the inner surface of the metal band. If themain portion extends further astern than the latter cylindrical surface,the protruding part does not have greater dimensions than to allow themetal band to be slipped onto this part up to the cylindrical surface.

Like in the alternative embodiment, this protruding part can be arrangedwith means for the joint of the type as will be mentioned below.

In the soldering or brazing operation, the band is arranged against thisshoulder so as to form a slot having a suitable thickness, about 0.2 mm,between the surfaces. As a result, the fixing with, for instance, silverfillers as brazing material will be strong. The soldering or brazing ispreferably carried out in such a manner that in any case the rear partof the entire front main portion is heated to the melting temperature ofthe soldering or brazing material.

According to the invention, it is also suggested that the projectilebody be arranged such that, in the assembled state thereof, the rearmain portion is arranged to extend into abutment against the rear flanksurface of the band, or at least to the vicinity thereof at diameterwhich essentially corresponds to the diameter of the circumferentialsurface of the projectile. This can be carried out, for instance, by therear main portion being provided with a forwardly directed annular flanksurface having an outer diameter which essentially corresponds to thediameter of the shell of the projectile and which, at least in its outerannular part, is positioned, when the body is assembled, so as to abutagainst or in the vicinity of the rear flank surface of the band. Thiseliminates any unnecessary air resistance caused by the band.

The main portions are connected to each other by means of, for instance,a threaded joint, an overlap joint or fixing screws, for instancedirected forwards from the stern. An overlap joint usually comprises atubular part of the front or rear main portion. This tubular part isinserted with a fit inside a likewise tubular part of the other mainportion. A joint may comprise some sort of guide means against spinning,e.g. splines together with break pins for locking in the axialdirection. The main portions can also be soldered or brazed together.This joining can then be effected while the band is soldered or brazedon. The joining means can be comprised in the projectile ahead of theband inside this like in the preferred embodiment, or behind this likein the alternative embodiment.

Advantages

The fixing of the band withstands high loads, by the band having a largefixing surface to the projectile body and by this surface being partlyarranged transversely of the direction of the resultant force from thepressure exerted by propellant gases on the rear flank surface of theband. This prevents this part of the fixing surface from being subjectedto the shear stress that is caused by the propellant gases oncylindrical fixing surfaces and that is added to the shear stress causedby the above-mentioned indisposition to spinning of the projectile.

The band is fixed to the heaviest main portion of the projectile, whichis favourable from the point of view of strength.

The band can be finished before being fixed. When fixing in prior-artmanner, the band must be machined after being fixed by pressing, forinstance by turning.

The projectile body is not subjected to the pressure arising if the bandis fixed by pressing, which may complicate the manufacture especially ofhollow projectile bodies. Nor is the projectile body subjected to localoverheating like in resistance welding, which is detrimental from thepoint of view of strength.

DESCRIPTION OF THE FIGURES

A preferred embodiment will now be described in more detail withreference to the accompanying Figures, in which the reference numeralsdesignate corresponding parts in both Figures.

FIG. 1 is a longitudinal section of the rear part of a projectile bodywith a fixed band.

FIG. 2 is a longitudinal section of the rear part of an alternativeembodiment of a projectile body with a fixed band.

FIG. 3 is a longitudinal section of the rear part of a projectile bodywith a fixed band, showing a gap between a rear flank surface of a bandand a forwardly directed annular flank surface of a rear main portion.

PREFERRED EMBODIMENT

FIG. 1 illustrates the rear part of a load-carrying projectilecomprising a hollow projectile body of forged steel, which is dividedinto a front main portion 1 and a rear main portion 2. The main portionsare joined by means of a threaded joint 3, but could also be joined bymeans of, for instance, an overlap joint. A band 4 of a copper alloy isarranged on the projectile body in connection with the joint between themain portions.

A stepped shoulder is formed in the end of the front main portion. Theshoulder consists of an annular flat flank surface 5 and a cylindricalsurface 6, with a fillet in the transition between the surfaces. Theband 4 is fixed by means of a brazing solder 7, such as a silver filler,to these surfaces. The band has an inner cylindrical surface 8 having adiameter exceeding that of the cylindrical surface 6 of the shoulder tosuch an extent that a brazing slot of 0.2-0.3 mm is obtained. The slotcan be kept in the brazing operation by means of a brazing fixture or bythe brazing surfaces of the band being provided, during manufacture ofthe band, with knobs 16, or small projections. The cylindrical surface 6of the shoulder is made so long that the abruptly cut-off, annular endface 9 of the front main portion and the flat annular rear flank 10 ofthe band reach astern to the same extent when the band has been brazedon. By means of, for instance, knobs, a brazing slot is obtained alsobetween the flank surface 5 of the shoulder and the front flank 11 ofthe band.

The rear main portion is formed with an annular flat flank surface 12,whose outer diameter is slightly smaller than that of the flat flanksurface 5 of the shoulder, and with a threaded cylinder 13 which isdirected forwards from the area inside the flank surface and whosethread matches an inner thread formed in the end of the front mainportion to constitute the threaded joint 3. After joining of the twomain portions, the flank surface 12 of the rear main portion abutsagainst the end face 9 of the front main portion as well as the rearflank 10 of the band. This design results in a very strong fixing of theband and an area, reinforced by the threaded joint inside the band, of aprojectile body portion which is subjected to great stresses. Thesestresses arise, for instance, when the grooves are pressed into the bandin the firing of the projectile.

FIG. 2 illustrates the rear part of an alternative projectile body whichis also divided into a front main portion 1 and a rear main portion 2.The main portions are joined by means of an overlap joint 14, locked bya number of breakable pins 15. The projectile can be used, for instance,as carrier of subwarheads, which are discharged in flight from the frontmain portion 1 after blasting away of the rear main portion 2. A band 4is fixed by brazing to the front main portion in the same fashion as inthe main embodiment.

In FIG. 3, rear flank 10 of the band 4 extends to the vicinity of flanksurface 12 of the rear main portion 2 to form a gap 20 located betweenrear flank 10 and flank surface 12. In gap 20 there are no connectionsbetween rear flank 10 and surface 12.

What is claimed is:
 1. A spin stabilized projectile comprising:aprojectile body with a front main portion and a rear main portion joinedby a joint, the front main portion having a rearwardly directed annularflank surface and a substantially cylindrical surface at a stern end,the substantially cylindrical surface having a first diameter; and apreformed solid band having a substantially cylindrical inner surface, arear flank surface and a front flank surface, the inner surface defininga second diameter larger than the first diameter such that said solidband is slipped over the stern end of said front main portion; anL-shaped slot defined between the substantially cylindrical surface ofthe front main portion and the inner surface of the band arid betweenthe front flank surface of said band and the rearwardly directed annularflank surface of the front main portion so that said inner surface issecurely attached by one of soldering and brazing in the slot to thesubstantially cylindrical surface of said front main portion, and thefront flank surface of said band is securely attached by one ofsoldering and brazing in the slot to the rearwardly directed annularflank surface of said front main portion, said soldering or brazingbeing only in said slot; said rear main portion being joined to saidfront main portion after said band has been slipped over the stern endof said front main portion and securely attached thereto; said rear mainportion having a forwardly directed annular flank surface extending inthe vicinity of the rear flank surface of the band which forms a gapbetween the forwardly directed annular flank surface and the rear flanksurface of the band in the absence of any connection including one ofsoldering and brazing for reducing air resistance caused by the band. 2.The spin-stabilized projectile as claimed in claim 1 wherein, when saidband is slipped over the stern end of said front main portion and, theslot between the substantially cylindrical surface of the front mainportion and the inner surface of the band is approximately 0.2 mm to 0.3mm.
 3. The spin-stabilized projectile as claimed in claim 1 wherein,when said band is slipped over the stern end of said front main portion,and the slot between the front flank surface of said band and therearwardly directed annular flank surface of the front main portion isapproximately 0.2 mm to 0.3 mm.
 4. The spin-stabilized projectile asclaimed in claim 2, wherein said band includes a plurality of knobs onthe inner surface to form the slot between the substantially cylindricalsurface of the front main portion and the inner surface of the band. 5.The spin-stabilized projectile as claimed in claim 1, further comprisinga plurality of knobs on the front flank surface of said band in the slotbetween the front flank surface of said band and the rearwardly directedannular flank surface of the front main portion.
 6. A spin stabilizedprojectile comprising:a projectile body with a front main portion and arear main portion joined by a joint, the front main portion having astern end with a first attaching surface substantially transverse to aresult-ant force from pressure exerted by propellant gases on saidprojectile body, and a second substantially cylindrical attachingsurface, said second attaching surface having a first diameter; apreformed solid band having a substantially cylindrical inner surface, afront flank surface and a rear flank surface, the inner surface defininga second diameter larger than the first diameter such that saidpreformed solid band is slipped onto the stern end of said projectilebody from behind; and an L-shaped slot of approximately 0.2 mm to 0.3 mmlocated between the inner surface of said preformed solid band and thesecond substantially cylindrical attaching surface of the projectilebody and between the front flank surface of said band and the firstattaching surface of the projectile body; said solid band being securelyattached through one of soldering and brazing in said slot to the sternend of said projectile body along only said first attaching surface andsaid second attaching surface; said rear flank surface of said bandextending in the vicinity of said rear main portion of said projectilebody which forms a aap between said rear flank surface of said band andsaid rear main portion of said projectile body in the absence of anyconnection including one of soldering and brazing for reducing airresistance caused by said band.
 7. The spin-stabilized projectile asclaimed in claim 6, further comprising a plurality of knobs on the innersurface of the bank in the slot between the second diameter and thefirst diameter.